The proposed study has the primary objective of investigating the transport and deposition of hygroscopic aerosols in the human respiratory tract, using physical models of the tracheobronchial tree. Emphasis will be placed on local deposition patterns. The proposed study is both experimental and theoretical in nature. In the experimental part, physical models of the tracheobronchial tree will be used to investigate the effects of particle size, chemical composition of the particles, and air flow on deposition rates. In the theoretical analysis, the problems of flow and particle deposition in well-defined successive bifurcations will be investigated. In addition, the effects of surfactants on the growth and evaporation of droplets will be studied. The long-term objective of the project is to develop a mathematical model for predicting the local and total deposition of hygroscopic particles in the human airways. The predictive model should have application in aerosol therapy.